Plastic based laminates comprising outer fiber-reinforced thermoset sheets, lofted fiber-reinforced thermoplastic sheets and a foam core layer

ABSTRACT

A light weight, high strength laminate having improved fire resistant characteristics and the method of making the same. A preferred embodiment includes a low density fiber reinforced thermoplastic resin core between two parallel sheets of high density fiber reinforced thermoset resin. Another embodiment includes a core of polymeric foam laminated between two parallel inner fiber reinforced thermoplastic resin layers each of which face an outer layer of fiber reinforced thermoplastic resin.

TECHNICAL FIELD

This invention is directed to light weight, high strength laminateshaving improved fire resistant characteristics and more particularly tolight weight, high strength laminates of high density, fiber-reinforcedthermoset resin, and low density thermoplastic resin, and the method ofmaking the same.

BACKGROUND OF THE INVENTION

Laminates are well known in the art, particularly for use asprefabricated building panels. Composite panels, such as those disclosedin U.S. Pat. No. 3,331,174, provide light weight economical structures,wherein a stiff foam core fills the area between two parallel fiberreinforced plastic sheets spaced apart by spacing members. The foam isadhered to the inner surface of each plastic sheet as well as to eachspacing member. However, such spacing members contribute to the weightof these prior art composite panels. Conventional materials used inprefabricated structures, such as wood, plywood, particle board ororiented strand board, as well as laminates such as those mentionedabove, while providing sufficient levels of strength and economy,generally exhibit a low level of fire resistance.

Light weight, high strength fire resistant structures having acompressed fiber reinforced thermoplastic layer covering a foam orwooden substrate are known in the art. When exposed to temperaturesnormally experienced in a fire, the fiber reinforced thermoplastic layerexpands or "lofts" to twice its original thickness, thus creating a firebarrier protecting the substrate. Although these lofted thermoplasticmaterials combine stiffness and strength with both light weight and highfire resistance, the surfaces of the lofted thermoplastic structures areporous. The porous nature of such materials is disadvantageous for useas building panels because it permits water absorption; it provides apoor surface for repainting; and it results in poor insulatingproperties.

SUMMARY OF THE INVENTION

It is the primary object of the present invention to provide improvedlight weight, low density, high strength, fire resistant laminates.

It is another object of the present invention to provide a laminatewhich possesses the stiffness, strength and fire resistance of thelofted, fiber-reinforced thermoplastic laminates without the porositygenerally characteristic of such materials.

Another object of the present invention is to provide improved lightweight, low density, high strength, fire resistant laminates which actas barriers to air and moisture and which have surfaces suitable for theapplication of coatings.

It is an object of the present invention to provide a structurepossessing the superior properties of the aforementioned lofted fiberreinforced thermoplastic material which also has a paintable surfacecapable of acting as an air and moisture barrier.

It is a further object of the present invention to provide high strengthlaminates of simplified design without spacing members.

It is another object of the present invention to provide a method ofmaking the aforementioned laminates.

These and other objects of the present invention are achieved byproviding a low weight, high strength laminate having two spacedparallel sheets of fiber-reinforced thermoset resin and at least onelayer of fiber-reinforced lofted thermoplastic resin laminated betweenthe two parallel sheets of fiber reinforced thermoset resin. In certainembodiments, the objects of the present invention are also achieved byplacing a core layer of polyphenylene ether, polystyrene or polyurethanefoam or mixtures thereof within the fiber-reinforced, loftedthermoplastic resin.

In another aspect of the present invention, there is provided a methodof making a low weight, high strength laminate wherein a layer of fiberreinforced thermoplastic resin capable of being lofted is placed betweentwo sheets of fiber reinforced thermoset resin to form a composite. Thecomposite is pressed at an elevated temperature for a sufficient time tocompact the layers thereby forming a laminate. The pressure is thencontrollably released from the laminate, at the elevated temperature,forming a laminate having a lofted fiber reinforced thermoplastic core.

In another aspect of the method of the present invention, after thepressure is controllably released from the laminate at the elevatedtemperature, the laminate lofts while cooling to room temperature, andthereafter a polymeric foam, such as a polyphenylene ether-polystyrenefoam blend, polystyrene foam, polyurethane foam or a mixture thereof, isplaced adjacent the thermoset layers of two parallel laminates eachhaving a thermoplastic layer and a thermoset layer and are thereafterpressed in a preheated press having mechanical stops on either sideuntil the foam bonds to the thermoplastic layers. After the form hasbonded to the thermoplastic layers, the temperature is lowered toambient and the pressure is released.

In one embodiment of the present invention there is provided a laminatehaving a core of glass fiber reinforced thermoplastic resin between twoparallel sheets of glass fiber reinforced thermoset resin. A furtherembodiment having even lower weight and increased resistance has apolyphenylene ether polystyrene blend, polystyrene, or polyurethane foamcore between two parallel inner thermoplastic layers, each of which facean outer layer of glass cloth prepreg polyphenylene ether epoxythermoset resin.

The present invention provides an improved laminate for use, forexample, as building panels in the modular home segment of theconstruction industry. The fabrication of a laminate having high densityouter skin layers and a low density lofted fiber reinforcedthermoplastic core enhances the effective stiffness per unit weight,strength, and fire resistance, as well as, reduces the weight ofprefabricated construction materials. Furthermore, the thermoset outerlayers not only improve the chemical resistance of the buildingmaterial, but also decrease the porosity, thereby creating an air andvapor barrier.

Other objects and advantages of the present invention will be apparentfrom the following Detailed Description and the accompanying drawings.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a cross sectional view of a 3 layer laminate in accordancewith the present invention;

FIG. 2 is a cross sectional view of a 5 layer laminate in accordancewith the present invention;

FIG. 3 is a cross sectional view of an alternate 5 layer laminate inaccordance with the present invention; and

FIG. 4 is a cross sectional view of a seven layer laminate in accordancewith the present invention.

DETAILED DESCRIPTION OF THE PRESENT INVENTION

Referring now to the drawings, wherein like reference numerals designatelike or corresponding elements throughout the views and particularlyreferring to FIG. 1, there is shown laminate 10 of the present inventionhaving layer 2, a fiber reinforced thermoplastic material, between twoparallel sheets of fiber reinforced thermoset resin 1 and 1a. Laminate10 is formed by pressing a composite, which includes layer 2 disposedbetween two parallel sheets 1 and 1a, at an elevated temperature for asufficient time to compact the layers and then controllably releasingpressure from laminate 10. Preferably, the composite is pressed betweenabout 500 p.s.i. and about 1500 p.s.i. at a temperature between about210° C. and 300° C. from about 10 minutes to about an hour. In oneaspect of the present invention the composite is pressed between platensof a press. At the elevated temperature the pressure is released fromthe composite by opening the platens of the press a predetermineddistance, preferably between about 1/2 inch and about 5/8 inch, therebyallowing Layer 2 to expand and fill the opening while cooling to roomtemperature.

In FIG. 2 there is shown a laminate 20 which is laminate 10 covered onat least one side by an outer layer 4 and optionally covered on theopposite side by an outer layer 4a. Layers 4 and 4a are a crosslinkedacrylate elastomer, a crosslinked styrene acrylonitrile copolymer, and alinear styrene acrylonitrile available from General Electric Companyunder the trademark Geloy, discussed in more detail below.

FIG. 3 shows a laminate 30 in which a polyphenylene ether-polystyrenefoam blend, polystyrene, or polyurethane foam layer 3 is disposedbetween layers 2 and 2a. Layer 3 may be placed adjacent thethermoplastic layers of two parallel lofted laminates, each having athermoplastic layer and a thermoset layer. The thickness of the layersmay vary. Preferably layers 2 and 2a are of equal thickness,symetrically sandwiching layer 3. Layer 3 may be adhesively bonded tolayer 2 by pressing the layers in a preheated press, with mechanicalstops on either side of the composite until the foam bonds to eachthermoplastic layer and then cooling, thereby forming a low weight highstrength laminate. Preferably the adhesive is a hot melt adhesive with amelting point between 80° C. and 120° C. The hot melt adhesive filmavailable from Shell Chemical, Inc. under the tradename Krayton FG 1901Xis highly preferred.

FIG. 4 shows a laminate 40, which is laminate 30 covered on at least oneside by an outer layer 4 and optionally on the opposite side by layer4a. Layers 4 and 4a are Geloy cladding discussed in more detail below.

The fire resistant fibers 5, used in the laminates of the presentinvention, are preferably in the form of single discrete fibers andpreferably have a high modulus of elasticity. The fire resistant fiberspreferably neither melt nor lose their high modulus of elasticity attemperatures below about 400° C., and more preferably at about 600° C.Suitable fibers include glass, carbon (graphite), silicon carbide,mineral and other ceramic fibers and certain polymeric fibers, such asaramid fibers sold under the trade names Kevlar and Nomex. Preferably,the fibers have a modulus of elasticity higher than about 10,000 MegaPascals.

Suitable fibers have at least about 50% by weight fiber strands having alength between about 0.125 inch and about 1.0 inch, more preferablybetween about 0.125 inch and about 0.5 inch, and most preferably about0.5 inch. The fibers preferably have an average diameter of from betweenabout 2 microns and about 30 microns, more preferably between about 12microns and about 23 microns and most preferably about 16 microns. Fiberlength is important in providing a desired level of lofting in structureupon exposure to heat. Fibers which are either too long or too shortprovide inadequate levels of lofting. Fiber diameters are important inproviding the desired levels of fiber stiffness. Fibers which are toothin lack the desired levels of stiffness for lofting and fibers whichare too thick are also generally too stiff and break during compression.

In layers 2 and 2a the binder material is an organic thermoplasticmaterial, which upon consolidation forms a solid matrix serving to bondthe fibers together in the composite layer. Suitable thermoplasticmaterials for forming a binder matrix include polyolefins, polyesters,polyamides, polyethers, polycarbonates, acrylonitrile styrene-butadienecopolymer, polyvinylchloride, and polystyrenes.

Suitable polyolefins include a polymerization product of at least onealiphatic ethylenically unsaturated monomer and are selected frompolyethylene and other polyolefins and copolymers of such monomers, forexample, polyethylene, polybutene, polypropylene, polypentene,poly(methylpentene), normally solid copolymer of ethylene and butene-1,copolymers of ethylene and ethyl acrylate, or vinyl acetate, butadiene-acrylonitrile copolymers, ionomers, poly(methyl methacrylate),polyisobutylene rubbers and the like, poly(vinyl chloride),poly(vinylidene chloride), a copolymer of vinyl chloride with vinylacetate, natural rubber, a rubbery copolymer of butene-1 and ethylene, arubbery copolymer of butadiene and acrylonitrile, and the like. All suchpolymers are commercially available or can be prepared by techniqueswell known to those skilled in the art. As to the copolymers andterpolymers, the proportions of the repeating units may vary broadly andwill be selected to provide the desired characteristics, i.e., normallyrubbery, normally solid, and the like. In addition to the polymersillustrated above, other suitable polymerization products of aliphaticethylenically unsaturated monomers include derivatives thereof, such ashalogenated hydrocarbon polymers, e.g., chlorinated polyethylene,chlorosulfonated polyhydrocarbons and polymerized carboxy-substitutedbutadiene and the like.

Other preferred thermoplastics are selected from polyacetalhomopolymers, such as polyoxymethylene, polyacetal copolymers, such asthose based on trioxane, polyphenylene ethers, such aspoly(2,6-dimethyl-1,4-phenylene)ether, polysulfones, such as thecondensation product of bisphenol A and 4,4'-dichlorodiphenyl sulfone,polyamides, such as polycaprolactam, or the product ofhexamethylenediamine an adipic acid, polyimides, e.g., the product ofbismaleimido diphenyl methane and methylene dianiline, normally solid ornormally rubbery polyorganosiloxanes, such as polyalkyl oraryl-siloxanes, or combinations of the two, and copolymers ofpolyorganosiloxanes with vinyl aromatics, e.g., styrene, acrylicmonomers, e.g., methyl methacrylate, or aromatic esters, e.g., thereaction products of bisphenol A and iso or terephthaloyl chloride, aswell as siloxane-nitrogen copolymers containing amido, amide-imido andimide groups. All such polymers are either commercially available or canbe made in ways known to those skilled in the art.

Also preferred are thermoplastics which comprise mixtures of any of theabove-mentioned thermoplastics. For example, one such mixture wouldcomprise a high molecular weight composition which is a combination ofpolystyrene or other styrene resin, including rubber modifiedpolystyrenes with a condensation product of 2,6-dimethylphenol, i.e.,poly(2,6-dimethyl-1,4-phenylene)ether.

Typical of the polyester resins suitable for this invention arepoly(alkylene terephthalates, isophthalates or mixed terephthalates andisophthalates), wherein the alkylene groups contain from 2 to 10 carbonatoms. They are available commercially or can be prepared by knowntechniques, such as by the alcoholysis of esters of the phthalic acidwith a glycol and subsequent polymerization, by heating glycols with thefree acids or with halide derivatives thereof, and similar processes.These are described in U.S. Pat. Nos. 2,465,319 and 3,047,539 andelsewhere.

Although the glycol portion of such typical polyesters can contain from1 to 10 carbon atoms, e.g., 1,2-ethylene, 1,3-propylene, 1,4-butylene,1,3-butylene, 1,2-propylene, 1,2-butylene, 2,3-butylene, 1,6-hexylene,1,10-decylene, etc., it is preferred that it contain 2 or 4 carbonatoms, in the form of linear methylene chains.

Preferred polyesters will be of the family consisting of high molecularweight, polymeric 1,4-butylene glycol terephthalates or isophthalateshaving repeating units of the general formula: ##STR1## and mixtures ofsuch esters, including copolyesters of terephthalic and up to about 30%isophthalic acids.

Especially preferred polyesters are polyethyleneterephthalate,poly(1,4-butylene 70/30 isoterephthalate) and poly(1,4-butyleneterephthalate). Special mention is made of the latter because it is easyto prepare from readily available materials and crystallizes at anespecially rapid rate.

Illustratively, sufficiently high molecular weight polyesters of thepreferred type will have an intrinsic viscosity of at least about 0.2and preferably about 0.4 deciliters/gram as measured in o-chlorophenol,a 60/40 phenol-tetrachloroethane mixture or a similar solvent at 25°-30°C. The upper limit is not critical, but will generally be about 1.5dl./g. Especially preferred polyesters will have an intrinsic viscosityin the range of about 0.5 to about 1.3.

Suitable aromatic polycarbonate resins are the polymers derived from abivalent phenol and a carbonate pre-product, for example phosgene, ahalogen formate or a carbonate ester. The aromatic polycarbonate resinspreferably possess an intrinsic viscosity of approximately 0.35-0.75(measured in p-dioxane at 30° C. and expressed in deciliters per gram).Suitable bivalent phenols which may be used for the preparation of thesearomatic polycarbonate resins are mononucleus and multinuclei aromaticcompounds which comprise 2-hydroxyl groups as functional groups whichare both directly bonded to a carbon atom of an aromatic nucleus.Examples of suitable bivalent phenols are: 2,2-bis(4-hydroxy-phenyl)propane (Bisphenol A=BPA), resorcinol; bis(4-hydroxy-5-nitrophenyl)methane; 2,2'-dihydroxydiphenyl; 2,6-dihydroxynaphthalene;bis-(4-hydroxy-phenylsulfone); 5'-chloro-2,4'-dihydroxyl-diphenylsulphone; 4,4'-dihydroxydiphenyl ether; and4,4'-dihydroxy-2,5-diethoxydiphenyl ether.

In preparing the aromatic polycarbonate resins it is possible to use twoor more different bivalent phenols or a copolymer of a bivalent phenolwith a glycol or with a polyester with a hydroxy or acid terminal group.The aromatic polycarbonate resin may also be prepared in the presence ofa dibasic acid. Crosslinked polycarbonate resins as described in U.S.Pat. No. 4,001,184 are also suitable. It is also possible to use amixture of two or more of the above-mentioned polycarbonate resins. Thehomopolymer derived from bisphenol A is preferably used as apolycarbonate resin.

Upon exposure to heat and flames, the binder material burns, decomposesor experiences reduced viscosity resulting in the release of the fiberweb allowing the web to loft. Generally, the longer the fiber length forrandomly dispersed glass fibers, the greater the web will loft and thegreater the web will protect the substrate. In other words, the longerthe fibers in a randomly dispersed compressed fiber system, the greaterthe degree of loft obtained upon decompression. The compressed compositelayers are made by consolidating into a solid continuous form, by heatand pressure, an unconsolidated, lofted wed including randomly disperredfibers and binder material. The pressure causes the fibers to becompressed, and the heat, in the case of thermoplastic binder materials,serves to melt the thermoplastic, which then flows around the fibers andupon cooling forms a solid matrix which locks the fibers into acompressed state.

As mentioned above, the preferred binder materials are thermoplastics.Preferably, the thermoplastic is, prior to dispersion and consolidation,in the form of a fine powder or particulate. The plastics may also be ina needle or fibrous form prior to dispersion and consolidation. Thefibers and thermoplastic powder or particulates can be randomlydispersed to form a lofted web by any of various well known dispersionprocesses including dry blending, aqueous dispersion, latex dispersionand foam dispersion processes. Suitable processes are set forth inUnited Kingdom Patent 1,129,757, United Kingdom Patent 1,329,409,European Patent Application 0,148,760, European Patent Application0,148,761, U.S. Pat. No. 4,426,470, and U.S. Pat. No. 3,716,449, all ofwhich are incorporated herein by reference. Extrusion processesinvolving the mixing of fibers and thermoplastics are generally notsuitable, in that they lead to substantial breakage of the fibersresulting in fibers of insufficient length for the desired level oflofting. The above dispersion processes result in the formation of a webof randomly dispersed fibers in thermoplastic powder. The web isinitially an unconsolidated web which is in a generally uncompressedstate, lofted, and in the form of a mat. Defining the unconsolidated webas being in a generally X, Y plane, the randomly dispersed fibersgenerally have degrees of orientation in each of the X, Y and Zdirection, the Z direction being perpendicular to the XY plane. Whilethe fibers may be primarily oriented in the XY plane, they generallyhave some degree of orientation in the Z direction. Having a degree oforientation in the Z direction can facilitate the fibers being in alofted state giving the web an initial unconsolidated thickness and arelatively low volume of glass. Upon being compressed to a compressedstate, the fibers will, due to their high modulus of elasticity, exertforces in the Z direction in an effort to return the web to its initialunconsolidated thickness. Thus, when the unconsolidated web is heatedand compressed and then cooled, the binder matrix upon solidificationholds the compressed fibers in a compressed state thereby providing arelatively thin compressed composite layer. Later upon exposure of thecomposite layer to high levels of heat or flames, the binder matrixmelts or burns allowing the fibers to loft in the Z direction therebyforming a thick lofted web of heat resistant fibers which act as a heatand fire barrier. Preferably layer 2 has about 40% to about 60% byweight polyphenylene ether thermoplastic binder and about 40% to about80% by weight of a random dispersion of glass fibers.

Layers 1 and 1a have respective amounts of fire resistant fibers and athermoset resin. Suitable thermoset materials for forming layers 1 and1a of the laminate include polyesters, phenolics, epoxy andpolyphenylene ether/epoxy blends. In one embodiment of the presentinvention the thermoset sheets have about 27% to about 80% by weight ofepoxy of a polyphenylene ether epoxy blend and about 20% to about 73% byweight of glass fibers. In another aspect of the present invention thethermoset resin of the thermoset sheet is a phenolic modified epoxythermoset resin impregnated into cotton linter paper. Suitable thermosetsheets include about 30% to about 75% by weight of polyphenyleneether/epoxy prepreg and about 25% to about 70% by weight of woven ornonwoven glass cloth.

Layers 1 and 1a and layers 2 and 2a optionally have mineral fillers,preferably light weight and/or flame retardant. More preferably themineral fillers are aluminum trihydrate, magnesium hydroxide, ormixtures thereof.

Layers 4 and 4a, as mentioned above, are a material which includes about10% to about 50% crosslinked acylate elastomer, about 5% to about 35%crosslinked styrene-acrylonitrile copolymer, and about 15% to about 85%linear styrene-acrylonitrile copolymer; as disclosed in U.S. Pat. No.3,994,631 incorporated herein by reference.

In order that those skilled in the art may be better able to practicethe present invention, the following examples are given as illustrationsof the superior strength, stiffness, weight reduction, as well as theimproved thermal, moisture and flame resistance of the presentinvention. It should be noted that the invention is not limited to thespecific details embodied in the Examples.

EXAMPLES 1-6

Laminates were prepared by pressing the layers shown in Table 1 at apressure between about 500 psi and about 1500 psi for about 10 minutesto an hour, and then opening the platens of the press about 1/2" to 5/8"thereby allowing the thermoplastic or foam core to expand and fill theopening while cooling to room temperature.

                  TABLE I                                                         ______________________________________                                        Laminate Layers of Some Embodiments                                           of the Invention                                                              ______________________________________                                        EXAMPLE 1: GELOY CLADDING                                                                PPO/EPOXY Blend (110 g/SF)                                                    LOFTED THERMOPLASTIC PPO                                                      (880 g/SF)                                                         EXAMPLE II:                                                                              GELOY CLADDING                                                                GETEK 7628 PREPREG                                                            LOFTED THERMOPLASTIC PPO                                                      (880 g/SF)                                                         EXAMPLE III:                                                                             GELOY CLADDING                                                                GETEK 7628 PREPREG                                                            LOFTED THERMOPLASTIC PPO                                                      (110 OR 220 g/SF)                                                             KRATON ADHESIVE                                                               GECET LOW DENSITY FOAM                                             EXAMPLE IV:                                                                              GELOY CLADDING                                                                EPOXY PAPER PREPREG                                                           LOFTED THERMOPLASTIC PP                                                       (110 g/SF)                                                                    KRATON ADHESIVE                                                               EPS or GECET LOW DENSITY FOAM                                      EXAMPLE V: GELOY CLADDING                                                                EPOXY PAPER PREPREG                                                           KRATON ADHESIVE                                                               EPS LOW DENSITY FOAM                                               ______________________________________                                    

The Geloy cladding used was 10 millimeters in thickness and commerciallyavailable from General Electric Company.

The PPO/Epoxy blend was 68% polyphenylene oxide (PPO), commerciallyavailable from General Electric Company, 27% EPON 828, commerciallyavailable from Shell Chemical, 3% zinc stearate commercially availablefrom Witco Co., and 2% Epolite 2347, commercially available from HexcelCorp., compounded in Banbury at 200° F. and the granulated in powderthrough a 20 mesh screen. The PPO/Epoxy layer was 50% by weight resincombined with 50% by weight 1/2 inch T or G filament glass, commerciallyavailable from PPG Industries to form 110 g/ft. mat.

The lofted thermoplastic polyphenylene oxide layer was 50% by weightpolyphenylene oxide commercially available from General Electric Companyand 50% by weight 1/2 inch G filament glass fibers, commerciallyavailable from PPG Industries. The total weight per square foot rangesfrom about 100 grams to about 880 grams. This layer was made by pressinga PPO/epoxy layer at 500 psi, 265° C., for 10 minutes, then releasingpressure and opening platens 1/2" (or 5/8") until cooled.

The GECET prepreg was 7628 glass cloth, commercially available from BGFIndustries, impregnated with a polyphenylene/epoxy resin blend, and thendissolved in toluene and dried at elevated temperature. The resincontent was about 40% to 45%.

The GECET low density foam is a blend of about 35% to about 50%polyphenylene oxide and 50% to about 65% of polystyrene, commerciallyavailable from General Electric Company, as extruded foam or expandedbead board.

A commercially available construction grade EPS low density foam,weighing 0.7 pounds per cubic foot, was compressed from 4.5 inches ofthickness to a core less than 1/2 inch thick.

The Kraton adhesive FG1901X, was commercially available from ShellChemical in 4 to 5 mil films cast from VM & P Naphtha solution.

The Epoxy Paper prepreg was 16063 paper prepreg, commercially availablefrom General Electric Electromaterials Company. It consisted of aphenolic modified epoxy formulation impregnated into 20 mil cottonlinter paper. The resin content was approximately 60%.

The lofted thermoplastic polypropylene was approximately 50%polypropylene commercially available from Himont Company and 50% 1/2inch M filament glass commercially available from PPG Industries.

Table II shows a comparison of mechanical properties of laminatesaccording to the present invention with commercially available 3-plyplywood, 5-ply plywood, and oriented strand board, as well as,conventional lofted thermoplastic composites.

                                      TABLE II                                    __________________________________________________________________________    PROPERTIES OF LAMINATE CONSTRUCTIONS                                                                                  SPECIFIC                                                                             SPECIFIC                                   DENSITY                                                                             THICKNESS                                                                             FLEX MOD                                                                             FLEX STR                                                                             STIFFNESS                                                                            STRENGTH                                   (LBS/CF)                                                                            (INCHES)                                                                              (Mpsi) (Mpsi) L  C   L  C                           __________________________________________________________________________    3 Ply Plywood                                                                             41    0.38     1400-L**                                                                            10-L   1.0                                                                              10.4                                                                              1.0                                                                              3.3                                                    135-C**                                                                              3-C   0.1                                                                              1.0 0.3                                                                              1.0                         5 Ply Plywood                                                                             34    0.49    870-L   6-L   1.1                                                                              11.3                                                                              0.7                                                                              2.4                         ORIENTED STRAND                                                                           42     0.225  450-L  2.5-L  0.3                                                                              3.1 0.3                                                                              0.8                         BOARD       41    0.44    500-L  2.5-L  0.4                                                                              3.3 0.3                                                                              0.8                         LOFTED      45    0.38    415    7.4    0.2                                                                              2.3 0.6                                                                              2.0                         THERMOPLASTIC                                                                 EXAMPLE I                                                                     (T GLASS SKIN)                                                                            47    0.49    590    9.9    0.3                                                                              2.9 0.8                                                                              2.5                         (G GLASS SKlN)                                                                            38    0.59    270    4.3    0.2                                                                              2.5 0.5                                                                              1.7                         EXAMPLE II  41    0.48    500    5.2    0.4                                                                              3.7 0.5                                                                              1.7                         EXAMPLE III                                                                   (220 g LOFTED R)                                                                          33    0.51    340    3.9    0.5                                                                              4.8 0.6                                                                              2.0                         (110 g LOFTED R)                                                                          26    0.50    315    4.2    0.9                                                                              9.1 1.1                                                                              3.5                         (110 g LOFTED R)                                                                          24    0.49    235    2.1    0.8                                                                              8.7 0.6                                                                              2.0                         EXAMPLE IV                                                                    (GECET CORE)                                                                              22    0.48    160    2.2    0.7                                                                              7.7 0.8                                                                              2.6                         (EPS CORE)  24    0.49     75    1.6    0.3                                                                              2.8 0.5                                                                              1.6                         EXAMPLE V   12    0.48     30    0.2    0.8                                                                              8.9 0.2                                                                              0.8                         (EPS CORE)                                                                    __________________________________________________________________________     R = LOFTED THERMOPLASTIC LAYER                                                *Specific Stiffness = Comparison of flexural modulus (FM) of material         normalized to density of 3 ply plywood (41 lbs./cu. ft.) = FM.sub.matl        /FM.sub.plywood (DENSITY.sub.plyw                                             Specific Strength = Comparison of flexural strength (FS) of material          normalized to density of 3 ply plywood (41 lbs./cu. ft.) = FS.sub.matl        /FS.sub.plywood * (DENSITY.sub.plyw                                           **" L" along the grain direction, "C" perpendicular to grain.            

As illustrated by the data in Table I the laminates of the presentinvention, Examples 1-5, exhibit increased strength and stiffness ascompared with conventional materials used in prefabricated structuressuch as 3 ply and 5 ply plywood, oriented strand board, and loftedthermoplastic resin.

Obviously, other modifications and variations of the present inventionsare possible in light of the above teachings. It is therefore to beunderstood that changes may be made in particular embodiments of theinvention described which are within the full intended scope of theinvention as defined by the claims.

What is claimed is:
 1. A lightweight, high strength laminatecomprising:a. two spaced parallel sheets of fiber reinforced thermosetresin; b. at least two layers of fiber reinforced lofted thermoplasticresin laminated between the two parallel sheets of fiber reinforcedthermoset resin; and c. a core layer of polyphenylene ether-polystyreneblend, polystyrene or polyurethane foam or mixtures thereof disposedbetween the thermoplastic resin layers.
 2. A laminate according to claim1 wherein the core layer is adhesively bonded to the thermoplasticlayers.
 3. A laminate according to claim 2 wherein the adhesive is a hotmelt adhesive with a melting point between about 80° C. and about 120°C.
 4. A laminate according to claim 1 having an outer layer on at leastone side comprising about 10% to about 50% crosslinked acrylateelastomer, about 5% to about 35% crosslinked styrene-acrylonitrilecopolymer, and about 15% to about 85% linear styrene-acrylonitrilecopolymer.